Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 1997
Publication Date: N/A
Interpretive Summary: Cattle grubs are an important pest of cattle, responsible for economic losses to the cattle industry as a result of damage to meat and hides. Adult cattle grubs are short lived and are generally active during the winter and spring months when temperatures are low. Adults lay their eggs on the hairs of cattle, preferring the lower and hind regions. Egg development is temperature dependent with maximum development and survival occurring at 35 deg C, a temperature near that of their host animal's body temperature. However, with solar warming, host animal skin temperatures may exceed 35 deg C, sometimes reaching as high as 48 deg C. We developed a regression model which predicts host animal skin temperatures based on ambient temperatures. We then studied the effects of temperatures above 35 deg C on egg survival. Egg hatch decreased from 79% at 35 deg C to 0 at 39 deg C. Some eggs survived temperatures of 40 and 45 deg C, varying from 58 to 80% depending on the length of exposure to these temperatures. Exposures of 3 h or more at 50 deg C were lethal, while 66% of all eggs survived 1 h at 50 deg C. The upper thermal limit for egg survival at constant temperatures was between 38 and 39 deg C.
During periods of Hypoderma lineatum (De Villers) oviposition activity, ambient temperatures reached 28 deg C while bovine dermal temperatures (dorsal) exceeded 45 deg C. Egg hatch decreased linearly with increased constant temperatures from 79% at 35 deg C to 0% at 39 deg C. Egg hatch varied from 58 to 80% following 1, 3 or 5 h exposure to 40 or 45 deg C. Exposure of 3 h or more at 50 deg C were lethal, while 66% of all eggs survived 1 h exposure to 50 deg C. The upper thermal limit for survival at constant temperatures lies between 38 and 39 deg C, with about 53% survival at 37 deg C. Hypoderma lineatum eggs appear to be well adapted to upper temperature extremes encountered in nature.